1. Field of the Invention
The present invention relates to a communication terminal device and a communication method for performing turbo encoding processing with respect to data that should be transmitted in accordance with a 3GPP (3rd Generation Partnership Projects) mobile communication system as well as a transmission method of the communication terminal device, a reception method of the communication terminal device and a transmission and reception method of the communication terminal device. The present invention is applicable to error correction encoding processing which uses a turbo code of a communication processor in a portable terminal device.
2. Description of the Related Art
Hitherto, in data communication using mobile phone in the 3GPP mobile communication system, there has been employed a technology in which two systems of convolutional encoding are performed with respect to input data 11 which should be transmitted as an error correction code and turbo encoding processing is performed using a turbo encoder with in-block interleave performed on one of the two systems by an internal interleaver.
FIG. 1 is a block diagram showing an encoding circuit of a conventional method.
With respect to the input data 11 to be transmitted, a turbo encoder 10 includes: two systems of convolutional encoder, one of which has an adder 12, D flip-flops 13, 14, and 15 and an adder 16 and the other of which has an adder 20, D flip-flops 21, 22, and 23 and an adder 24; and a turbo internal interleaver 19 which performs the in-block interleave with respect to the other convolutional encoder.
In FIG. 1, in order to obtain a desired encoding rate, rate matching units 27 and 29 are used to thin out parity bits 18 and 25 which are output from the turbo encoder 10 based on a rate matching algorithm. The turbo encoder 10 converts both a system bit 17 in which the input data 11 is output without any change and the output from the rate matching units 27 and 29 from parallel data to serial data in a parallel-serial converter 30 to output an encoded output 31.
The encoding rate of the turbo code in the turbo encoder 10 can be set to various values according to various communication services. An adjustment of the encoding rate of the turbo code is performed by thinning out (puncturing) the output of the turbo encoder 10 through an application of a regulation established as the rate matching units 27 and 29, instead of changing the encoding rate thereof.
[Non-patent reference 1] (Name of Standard) 3GPP TSG-RAN Working Group 1#32, Paris, France, MAY 19-23, 2003, “R1-030421 Turbo Coder Irregularities in HSDPA.doc”, (online) [searched on Sep. 3, 2003] Internet <URL:http://www.3gpp.orgftp://ftp.3gpp.org/specs /2003-03/>
When the turbo encoding processing is performed in the above described turbo encoder 10, there has been an inconvenience in which turbo code performance becomes deteriorated in a specific encoding rate due to a relation between a generating polynomial of the turbo code and a puncturing pattern generated by the rate matching algorithm.
The above problem occurs noticeably when a puncturing rate is high and a cycle of the puncturing pattern is 7 bits as shown in the standard of the non-patent reference 1. This is attributed to the generating polynomial of the convolutional encoder which is used for the turbo encoder. In other words, when an arbitrary one bit to be input into the convolutional encoder is considered, an output bit not affected by the input bit appears at a 7-bit cycle as the output of the convolutional encoder. Although the above problem can be avoided either by changing the generating polynomial of the convolutional encoder or by changing the rate matching algorithm, there is a disadvantage of not utilizing an existing design asset.
Accordingly, the present invention aims to provide a communication terminal device and a communication method capable of not deteriorating the turbo code performance when the communication is performed at a specific encoding rate in the mobile phone in accordance with the 3GPP mobile communication system.